Key Points Resolving, but not hyperinflammatory stimuli create a microenvironment conducive for the optimal development of adaptive immunity. After onset and resolution, we introduce a third phase to acute inflammatory responses dominated by macrophages and lymphocytes.

IntroductionMigration of B cells into secondary lymphoid organs is required for an antigen-specific humoral immune response. B cells migrate from the bloodstream to lymph nodes by extravasation from high endothelial venules. The response to chemokines and integrinmediated adhesion to endothelial cells is a key step in this process. 1 B cells in secondary lymphoid organs are critical to homeostatic and inflammatory regulation of these tissues. If the lymph node becomes inflamed, B-cell migration is a prerequisite for normal hypertrophy and the further recruitment of dendritic and T cells. 2 B-cell trafficking within lymph nodes is also important during the generation of the germinal center reaction and humoral immune responses. [3][4][5][6] Abnormal chemoattractant-mediated B-cell migration is central to infiltration of malignant B cells into tissues and formation of ectopic germinal centers in autoimmune diseases. [7][8][9] The transduction of signals from cell surface receptors to the actin cytoskeleton to regulate cell adhesion and migration requires small G proteins of the Ras superfamily. [10][11][12] These include members of the Ras family, including Ras and Rap1, and members of the Rho family, such as Rac, Cdc42, and Rho. 13 Upstream activators of Rho proteins such as the Dbl homology domain proteins of the Vav family are required for ␤-integrin and chemokine-mediated Rac, Cdc42, and Rho activation and stable adhesions of cells. 14 Although B-cell migration is vital for their development, the pathways underlying integrin and chemokine signals in B cells are poorly defined. We identified the signaling protein SWAP-70 15 as required for B-cell migration and adhesion in vitro and in vivo. 16 Swap70 Ϫ/Ϫ B cells show aberrant integrin-mediated adhesion, defective polarization, and do not form uropods and stabilized lamellipodia in vitro. This leads to a defect in migration and homing of B cells to lymph nodes in vivo. In correlation with these defects in migration and adhesion, Swap70 Ϫ/Ϫ transitional B cells hyperadhere to the splenic red pulp and are impaired in differentiation into marginal zone B-cells. 17 In addition, Swap70 Ϫ/Ϫ B cells do not generate a normal germinal center response, 18 a process requiring high B-cell motility and a dynamic morphology, 6 which are most likely disturbed by the absence of SWAP-70.SWAP-70 interacts with and regulates proteins of the Rho family, in particular Rac and RhoA. 19,20 Unusually, SWAP-70 has a Dbl homology domain to the C-terminus of its pleckstrin homology (PH) domain. 20 The PH domain binds PIP 3 and SWAP-70 also binds F-but not G-actin. 20,21 The binding of SWAP-70 to F-actin depends on cell stimulation and is required for regulation of cytoskeletal rearrangements such as membrane ruffles. 21 Although its regulation of Rac and actin polymerization are likely to be important for SWAP-70's function in regulating B-cell migration, little is known about how SWAP-70 itself is regulated, other than its interaction with PIP 3 , which is required for its localization. ...

Most tissue-resident macrophages (Mφs) are believed to be derived prenatally and are assumed to maintain themselves throughout life by self-proliferation. However, in adult mice we identified a progenitor within bone marrow, early pro-B cell/fraction B, that differentiates into tissue Mφs. These Mφ precursors have non-rearranged B-cell receptor genes and coexpress myeloid (GR1, CD11b, and CD16/32) and lymphoid (B220 and CD19) lineage markers. During steady state, these precursors exit bone marrow, losing Gr1, and enter the systemic circulation, seeding the gastrointestinal system as well as pleural and peritoneal cavities but not the brain. While in these tissues, they acquire a transcriptome identical to embryonically derived tissue-resident Mφs. Similarly, these Mφ precursors also enter sites of inflammation, gaining CD115, F4/80, and CD16/32, and become indistinguishable from blood monocyte-derived Mφs. Thus, we have identified a population of cells within the bone marrow early pro-B cell compartment that possess functional plasticity to differentiate into either tissue-resident or inflammatory Mφs, depending on microenvironmental signals. We propose that these precursors represent an additional source of Mφ populations in adult mice during steady state and inflammation.

There is an increasing need to understand the leukocytes and soluble mediators that drive acute inflammation and bring about its resolution in humans. We therefore carried out an extensive characterisation of the cantharidin skin blister model in healthy male volunteers. A novel fluorescence staining protocol was designed and implemented, which facilitated the identification of cell populations by flow cytometry. We observed that at the onset phase, 24 h after blister formation, the predominant cells were CD16hi/CD66b+ PMNs followed by HLA-DR+/CD14+ monocytes/macrophages, CD11c+ and CD141+ dendritic cells as well as Siglec-8+ eosinophils. CD3+ T cells, CD19+ B cells and CD56+ NK cells were also present, but in comparatively fewer numbers. During resolution, 72 h following blister induction, numbers of PMNs declined whilst the numbers of monocyte/macrophages remain unchanged, though they upregulated expression of CD16 and CD163. In contrast, the overall numbers of dendritic cells and Siglec-8+ eosinophils increased. Post hoc analysis of these data revealed that of the inflammatory cytokines measured, TNF-α but not IL-1β or IL-8 correlated with increased PMN numbers at the onset. Volunteers with the greatest PMN infiltration at onset displayed the fastest clearance rates for these cells at resolution. Collectively, these data provide insight into the cells that occupy acute resolving blister in humans, the soluble mediators that may control their influx as well as the phenotype of mononuclear phagocytes that predominate the resolution phase. Further use of this model will improve our understanding of the evolution and resolution of inflammation in humans, how defects in these over-lapping pathways may contribute to the variability in disease longevity/chronicity, and lends itself to the screen of putative anti-inflammatory or pro-resolution therapies.

Asthma and allergies are major health concerns in which Ig isotype E plays a pivotal role. Ag-bound IgE drives mast cells and basophils into exocytosis, thereby promoting allergic and potentially anaphylactic reactions. The importance of tightly regulated IgE production is underscored by severe immunological conditions in humans with elevated IgE levels. Cytokines direct IgH class-switching to a particular isotype by initiation of germline transcription (GLT) from isotype-specific intronic (I) promoters. The switch to IgE depends on IL-4, which stimulates GLT of the Iε promoter, but is specifically and strongly impaired in Swap-70−/− mice. Although early events in IL-4 signal transduction (i.e., activation of the JAK/STAT6 pathway) do not require SWAP-70, SWAP-70 deficiency results in impaired Iε GLT. The affinity of STAT6 to chromatin is reduced in absence of SWAP-70. Chromatin immunoprecipitation revealed that SWAP-70 binds to Iε and is required for association of STAT6 with Iε. BCL6, known to antagonize STAT6 particularly at Iε, is increased on Iε in absence of SWAP-70. Other promoters bound by BCL6 and STAT6 were found unaffected. We conclude that SWAP-70 controls IgE production through regulation of the antagonistic STAT6 and BCL6 occupancy of Iε. The identification of this mechanism opens new avenues to inhibit allergic reactions triggered by IgE.

Background & AimsPatients with decompensated cirrhosis are susceptible to infection. Innate immune dysfunction and development of organ failure are considered to underlie this. A rodent model of liver disease sharing these phenotypic features would assist in vivo study of underlying mechanisms and testing of therapeutics. We evaluated three models to identify which demonstrated the greatest clinical and immunological phenotypic similarity to patients with acutely decompensated (AD) cirrhosis.MethodsWe selected Bile Duct Ligation (BDL) rats at 4 weeks, BDL mice at 14 days and Carbon tetrachloride (CCl4) mice at 10 weeks (with studies performed 7 days after final CCl4 infection). We examined organ dysfunction, inflammatory response to carrageenan‐in‐paw, plasma eicosanoid concentrations, macrophage cytokine production and responses to peritoneal infection.ResultsBile duct ligation caused sarcopenia, liver, cardiovascular and renal dysfunction whereas CCl4 mice demonstrated no clinical abnormalities. BDL rodents exhibited depressed response to carrageenan‐in‐paw unlike CCl4 mice. BDL rats have slightly elevated plasma eicosanoid levels and plasma showed partial PGE 2‐mediated immune suppression whereas CCl4 mice did not. Plasma NOx was elevated in patients with acute or chronic liver failure (AoCLF) compared to healthy volunteers and BDL rodents but not CCl4 mice. Elevated nitric oxide (NO) via inducible nitric oxide synthase (iNOS) mediates defective leucocyte trafficking in BDL rodent models.ConclusionsWe conclude that BDL mice and rats are not simply models of cholestatic liver injury but may be used to study mechanisms underlying poor outcome from infection in AD and have identified elevated NO as a potential mediator of depressed leucocyte trafficking.